RB Series Engine Oil Control

RB Series Engine Oil Control

Following on from this thread on Driftworks I thought I would post a definitive “UK Guide” to oil control on the RB series engines.
The Issues

Oil Control

In a nutshell, RB series engines suffer from oil control issues when exposed to consistently long periods of high RPM mixed with lateral G-Forces. The route of this problem centres around the engine pumping too much oil into the head at high revs and it not being able to escape back down into the block due to inadequate oil return passages. Thus, this oil with nowhere to often gets blown out into catch tanks or out of the cam breathers and into the inlet system to be burned and combusted. The result is an rotating assembly (crank/rods/pistons) robbed of oil and prone to failure.

Drive Collar

This problem affects the following engines

–          Early RB26DETT

–          RB30E & ET

–          RB20DET & DE

–          RB25DE & DET Series 1 & 2

–          RB25DET NEO (although this is a bit hit and miss)

The oil pump drive collar problem is caused by the contact area on the end (or snout) of the crank that mates with the oil pump drive on the oil pump gear being of inadequate size and prone to wear. This results in progressive wear that’s excepted by consistent high rpm. In many cases the crank drive often snaps or spins within the oil pump gear destroying the oil pump and giving zero oil pressure (usually at high RPM)

Snapped oilpump drive gear
Long nose collar on the left – short nose collar on the right

The Fixes

Oil Control

Correcting the oil control issues within an RB engine is a 5 step process –
Block off one oil feed in the block

On an RB series block there are two oil feed galleries on the inlet size of the block. The rear of these two needs to be completely blocked off to prevent excess oil flow to the head. The RB26DETT has this rear feed blocked off as standard. Any good machine shop should be able to do this for you.

The two oil feed galleries

Restrict the oil flow to the front oil feed gallery.

Using the chart below fit an appropriately sized restrictor to the other feed. The size of the oil pump is one of the determinates for the size of the restrictor, ie; a high flow, high pressure pump needs a smaller restrictor. Constant higher RPM needs a smaller restrictor etc. A restrictor can be purchased from Tomei  through Power House racing in the states (see link) for around £20 (sterling) but your machine shop should be able to knock you one up from brass for about 1/3rd of the price fitted. The existing oil restrictor can be knocked down further into the gallery when the new one if fitted.

Tomei Diagram
RB26 RB25/20 RB25
No VVT No VVT VVT
Front

Feed

Rear

Feed

Front

Feed

Rear

Feed

VVT Supply Front

Feed

Rear

Feed

Standard Pump
Road 1.5mm Block off 1.5mm Block off Leave Block off 1.5mm
Drag 1.25mm Block off 1.5mm Block off Leave Block off 1.5mm
Circuit/Drift 1.25mm Block off 1.25mm Block off Leave Block off 1.25mm
RB26 N1 Oil Pump
Road 1.5mm Block off 1.5mm Block off Leave Block off 1.5mm
Drag 1.25mm Block off 1.5mm Block off Leave Block off 1.5mm
Circuit/Drift 1mm Block off 1mm Block off Leave Block off 1mm
Aftermarket Oil Pump (Jun, HKS, Greddy, Apexi)
Road 1.25 Block off 1.5 Block off Leave Block off 1.5mm
Drag 1mm Block off 1.25 Block off Leave Block off 1.25
Circuit/Drift 1mm Block off 1mm Block off Leave Block off 1mm

Fit an external oil return from the rear of the cylinder head to the sump

To assist in returning any additional pooled oil from the head to the sump an external oil drain is added. Kits can be purchased from places like JDM Garage and GARAGE D which consist of an adaptor block that connects to the back of the head via a Welsh plug hole (remove Welsh plug first!) and a braided hose that connects to the sump. The vacuum pressure created by the crank rotating in the sump also serves to help equalise pressure in the head and felicitated oil return.

Spool rear oil drain

Drill out the oil return galleries in the head and block

The oil return galleries in the head and the block can be machined out to the edge of the gasket. This smooths out the galleries (badly cast) matches the head to the block. You can usually get about a 1mm on each gallery.

Machine around the oil return galleries to facilitate access for the oil

Pretty self explanatory, but in the top of the head you need to die grind the entry to the oil return galleries to allow the oil to enter them easier (instead of pooling)

Additional Precautions

Run a larger sump

It’s an expensive thing to do (having a custom sump made) and there are not really very many off the shelf solutions available. However a larger, baffled & winged sump is going to give you a much larger supply of oil on tap which is an added safeguard. It’s not essential, but it’s defiantly worth doing.

Large Sump

(Added at the suggestion of Zell from Driftworks. )

Oil Accumulator (Accusump)

The oil accumulator is a chamber that, as the name implies, accumulates pressurized engine oil. The accumulator holds it there until a time when oil pressure in the engine falls. Then, it feeds the oil back to the engine while the pump is rebuilding pressure. At this point, the pump also refills the accumulator and the cycle is ready to begin again. Keep in mind this may all happen in a fraction of a second. Again, this isn’t an essential as i rarely see oil surge on RB’s – but it’s a definite precaution.

Accusump

Oil Pump Drive Collar

This is a very simple fix that requires a good machine shop and an aftermarket crank collar. The existing oil pump drive on the crank is machined off and a crank collar is interference fit in its place. You can purchase these crank collars from SPOOL IMPORTS in Australia and any decent machine shop will fit them.

Spool Crank Collar…
Drive collar fitted

Chart courtesy of SYDNEYKID of the Skyline Australia board.

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8 thoughts on “RB Series Engine Oil Control

  1. Question. I’m in the middle of a build where I’ll be using a S2 built block and a NEO head. I noticed when I removed the head off the Neo engine there was no oil restrictor in the front intake side of the block but the S2 block has one. what should I do?

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